This application claims the benefit of Japanese Patent Application No. 2004-258740, filed Sep. 6, 2004. The entire disclosure of the prior application is hereby incorporated by reference herein in its entirety.
1. Technical Field
The present invention related to a semiconductor and a method of manufacturing a semiconductor, more particularly to a method for a chip size package (CSP) and a ball grid array (BGA.)
2. Related Arts
Conventionally, a method for using CSP or BGA has been used for downsizing a semiconductor package. In these methods such as CSP and BGA, a semiconductor package is formed by using a carrier substrate on which a semiconductor chip is mounted. Here, a carrier substrate is jointed to a mother-board by using a solder ball or a lead ball, when a carrier substrate, on which a semiconductor chip is mounted, is placed on a mother-board. Then, a land is formed in a carrier substrate and a mother-board, in order to joint a solder ball or a lead ball to a carrier board and a mother-board.
Here, copper is generally used as a material for a land on the substrate 21. Then a basis metal of a land is plated with nickel and gold in order to insure the strength of a ball shear and tolerance to temperature cycle. In recent years, a semiconductor package using CSP and BGA has been mounted on a mobile phone in response to a downsized and sophisticated mobile phone device. Under the situation, in order to improve tolerance to shock when falling a device, a solder ball or a lead ball is directly jointed to a basis metal of copper without nickel- or gold-plating a land.
Further, the Japanese unexamined patent publication 10-340972 discloses a method for forming an tapered end at the opening of a solder resist layer in order to avoid a crack to a solder ball when temperature cycling.
However, when a solder ball or a lead ball is directly jointed to a base of copper, there is problem of deteriorating the shearing strength (horizontal strength), the strength of a ball shear and tolerance to temperature cycle, even if tolerance to shock is improved when falling a device. On the other hand, when gold-plating a land, there is the other problem of deteriorating tolerance to shock when falling a device because of weakness toward peeling off direction of (Cu, Ni)6 Sn5 even if assuring the shearing strength, the strength of a ball shear and tolerance to temperature cycle.